Neuron loss, either dependent or independent of sensory hair cell loss, contributes significantly to hearing loss, particularly in the aging population. Future treatments, particularly stem cell therapies, will require detailed understanding of statoacoustic ganglion (SAG;VIIIth cranial nerve) developmental processes. We propose to analyze molecular and cellular mechanism of cadherin cell adhesion during zebrafish SAG development. SAG precursor cell behaviors will be studied using various assays, including advanced imaging methods to analyze proliferation, survival, maturation and SAG precursor cell movements from the otic vesicle to the forming ganglion. These experiments specifically fit the NIDCD Program Announcement PA-07-127. Overall hypothesis: the cadherin cell adhesion system responds to polarity cues and regulates morphogenetic cell movements during SAG development. Aim 1: Determine the expression pattern for cadherin-2, -4, -6 and -10 (cadherins expressed in the SAG) during normal and knockdown embryo SAG development. Cdh2, Cdh4 and Cdh6 knockdown experiments (nomenclature: gene names cdh2, cdh4, cdh6 and cdh10;and protein names Cdh2, Cdh4, Cdh6 and Cdh10) showed that these cadherins are required for SAG development. Cdh10 knockdown showed little or no SAG development phenotype, but this cadherin is expressed in a much smaller subset of SAG cells. We will examine spatial and temporal expression patterns for cadherin-2, -4, -6 and -10. We hypothesize that cadherin expression regulates SAG precursor cell movements, precursor cell survival and neuronal differentiation during inner ear development. Individual cadherin expression patterns will also be examined in Cdh2, 4, 6 and 10 knockdown embryos to determine whether there is compensatory cadherin expression. Aim 2: Determine cadherin signaling effects on SAG development. We hypothesize that cadherin activity regulates specific cellular phenotype (differentiation, growth, survival and migration) during SAG development. Signaling mechanisms will be compared using assays for otic specification, proliferation and survival. In addition, we propose to evaluate SAG precursor cell behaviors using state-of-the-art time-lapse imaging. Normal SAG development will be compared with cadherin loss-of-function phenotypes. In addition, cell polarity signaling molecule functions during SAG development will be studied. Aim 3. Determine whether specific cadherin activity that regulates SAG cell development is cell autonomous or non-cell autonomous. We hypothesize that cadherin activity can regulate different cellular phenotypes (e.g., differentiation, growth, survival and migration) cell autonomously and other cellular phenotypes cell-non autonomously during SAG development. Cell transplantation, genetic mosaic experiments will be performed to determine whether the molecular and cellular mechanisms that were identified act cell autonomously or cell-non autonomously. Nerve cell loss contributes to hearing loss, particularly in the aging population. Future treatments for hearing loss, especially the promise of stem cell therapies, will require detailed understanding of nerve development, including growth and maintenance of the auditory nerve. We propose a novel approach to the study of this process, which fits NIDCD Program Announcement PA-07-127.